1. Field of the Invention
The present invention relates to a charged-particle beam irradiation apparatus, a charged-particle beam rotary irradiation system, and a charged-particle beam irradiation method which are adapted to a therapeutic apparatus using a charged-particle beam or the like.
2. Description of the Related Art
FIG. 16 shows an example of a charged-particle beam rotary irradiation system that is a conventional therapeutic apparatus using a charged-particle beam disclosed in, for example, a report written by Pedroni of Switzerland (Medical Physics, Vol. 22, PP.37-53).
In the drawing, there are shown a charged-particle beam rotary irradiation system 100, a particle accelerator 1, a transporting electromagnet 3, an energy degrader 5, a proton beam 7, a beam stopper 9, a rotating gantry 10, deflective electromagnets 11, 13, and 19, convergent electromagnets 15, a scanning electromagnet.17, an energy degrader 21, a dose/position monitor 23, a patient 25, a radiation table 27, and an axis of rotation of the gantry 29.
A proton beam generated by the accelerator 1 is transported by the transporting electromagnet 3, passed by the energy degrader 5 serving as an initial-stage energy changing means, and thus recomposed into a proton beam 7 having given energy level. The proton beam 7 is deflected upward from a horizontal direction by the first deflective electromagnet 11, and then returned to the horizontal direction by the deflective electromagnet 13.
The proton beam 7 is converged by the convergent electromagnets 15, and swept vertically by the scanning electromagnet 17. The swept proton beam is deflected immediately downward by the last deflective electromagnet 19, and then irradiated to the patient 25 via the energy degrader for fine adjustment 21 and the dose/position monitor 23.
Herein, the electromagnets 11, 13, 15, 17, and 19, energy degrader 21, and monitor 23 are integrated into one unit, thus forming an irradiation gantry. The irradiation gantry can make a turn about the axis of rotation 29 and is referred to as the rotating gantry 10.
The spot of the proton beam irradiated to the patient 25 is shifted parallel to an X-axis direction alone shown in FIG. 16 by means of the scanning electromagnet 17 and deflective electromagnet 19. Scanning the patient in a Y-axis direction which is required for a therapeutic procedure is achieved by moving the radiation table 27. Scanning the patient 25 in a depth direction (Z-axis direction) of the patient 25 is achieved by adjusting the energy of the proton beam using the energy degrader 21.
The length of the rotating gantry 10 in the longitudinal direction thereof is approximately 10 m. A length in the gantry where the proton beam is displaced away from the gantry rotation axis 29 is approximately 2 m.
In the thus-configured conventional modality using a charged-particle beam, spot scanning in which the spot of a beam is shifted parallel to one axial direction alone (the X-axis direction in the above example) can solely be realized. The patient 25 must be moved in the Y-axis direction by moving the table 27 during treatment. This poses a problem that the movement gives the patient senses of discomfort and fear and results in displacement of a radiation area.
Moreover, in the above conventional modality, since the spot of a beam parallel to an axis of incidence thereof is shifted, the scanning electromagnet 17 must be placed upstream of the deflective electromagnet 19. Accordingly the deflective electromagnet 19 for deflecting a proton beam, i.e. the charged-particle beam, which is swept vertically by the scanning electromagnet 17, becomes large in size. As a result, the total weight of the treatment rotating gantry 10 becomes 100 tons or more. Moreover, since the deflective electromagnet 19 is so large as to have magnetic poles of several tens centimeters wide, when a superconducting magnet is employed, there arises a problem of very high manufacturing cost.